Study of genetic diseases with neoplastic manifestations and detailed investigation of families with high risk of cancer may help detect environmental and genetic influences in carcinogenesis, especially when appropriate laboratory assays are used. Besides results from the Clinical Studies Section, clinical reports were made on three cancer families and a series of patients with rhabdomyosarcoma complicating neurofibromatosis. Special emphasis was placed on laboratory approaches to cancer families. The heritability of SV40 T-antigen in 26 families and the frequencies of chromosomal abnormalities and sister chromatid exchanges in five families were reported. In one family with acute myelogenous leukemia, patients with malignancies had abnormal sensitivity of fibroblast to gamma-radiation, whereas tumor-free relatives had normal sensitivities. Abnormal in vitro response to pooled alloantigens was a consistent abnormality in family members with the B-K mole syndrome (and some spouses). We continue to seek animal models for human, congenital and genetic disease, and will follow the same approach, using new laboratory methods and epidemiologic clues from other sources as available.